Resonant cavity circuits



' Aug 1948. A. v. HAEFF RESONANT CAVITY CIRCUITS Original Filed Jan. 18,1941 4 Sheets-Sheet l I Z1 INPUT OUTPUT ANDREW V. H AEFF Aug. 1948. A.v. HAEFF RESONANT CAVITY CIRCUITS 4' Sheets-Sheet 2 Original Filed Jan.18, 1941 MOPUWZKU 4 Sheets-Sheet 4 E B r I $15M u IIEFIEIIIIIIIJ- A.VIHAEFF RESONANT CAVITY CIRCUITS Original'Filed Jan. 18, 1941 dO-PUMJJOUnflmu ok fix k E km 3 g a HQ 3% H g. m mm Mm V 5.. 3. mm RN NE. .U @m WM3110mm ANDREW V HAEFF Patented Aug. 17, 1948 UNITED" Es PATENT, OFFICEREsoNANr CAVITY CIRCUITS Andrew V. Haeff, Washin ton. D. C., assignortoRadio Corporation of America, a orporation 1 Delaware Originalapplication January 18,

1941, Serial a...

375,029. Divided and this application April 27. 1943, Serial No. 484,692

j lClaims. (Cl.178-'44) January 18; 1941, now Patent 2,399,223, issuedApril 30, 1946,- and assigned to the same assignee as the presentapplication. 1

It has been demonstrated that tubes utilizing conventional grids forcontrolling current are well adapted for operation at ultra-highfrequencies and retain their characteristic advantage ofpossessing hightransconductance. However, one of thedifiiculties encounteredinoperating amplifying tubes at ultra-highirequemcies is the presence ofconsiderable'loadin in the input circuit which results in an excessiveamount of power being required to drive the tube. l his decreases the'efiective power gain of the tube when operated as an amplifier.

The fundamental causes of high input loading are: (1) ohmic andradiation resistance losses due to high circulating currents inelectrodes and leads; (2) electron-loading which results fromtheinteraction of the electron stream with the circuit, includingdegenerative or regenerative effects caused by lead impedance.

In'orderto' reduce ohmic resistance losses it u is necessary ,to useinternal leads and external conductors made of high conductivitymaterial and having large peripheries. In addition interelectrodecapacitances must be reduced as much as possible in order to minimizecirculating currents. To'reduce radiation losses a thoroughly shieldedcircuit of conventional design or'closed type cavity resonators must beused.

The principal object oi my invention is to pro-- vide an electrondischarge device and associated circuithaving-means for substantiallyreducing or completely neutralizing electron loading when the device isused at ultra-high frequencies.

It is also an object of my invention to provide an electron dischargedevicehaving means for minimizing ohmic and radiation resistance losseswhenthe device is used at ultra-high frequencies.

A 'still further objectxof my invention is to provide improved forms ofresonant cavity tank circuits or resonators suitable for use with ultrahigh frequency electron discharge devices and means for tuning the same.

The novel features which I believe to be characteristic of my inventionare set forth with particularity in the appended claims, but theinvention itself will .bestbe understood by reference to the followingdescription taken in connection.

with the accompanying drawing in which Figures 1 and 2 are diagrammaticrepresentations of electrodes and the movement of electrons between theelectrodes; Figures 3 and 4 are diagrammatic representations ofconventional tubes and meth ods of operating the same; Figures 5 anddare curves representing the relationship of the electron loading(conductance) and the transit time of the-electrons of the tubes'inFi-guresii and 4; Figures 7 to 10 inclusive ,arediagrammaticrepresentations of tubes and=circuits made accordingv to my inventionforpraicticing my. invention; Figure 11 is a longitudinal section of anelectron discharge device, made according to my invention; Figure 11a isa section taken along the line Ilia-Ala of; Figure 11; Figures 12. and13 are.

longitudinal sections ofmodi'fications of an electron discharge devicemade according to my in vention. 3 V

In order to understand-better the effect of. electronloading, themechanism of interaction betweenthe electron stream and the electrodesto which circuits may be connected will be reviewed. Consider a systemof two electrodes ill and ll as shown in Figure 1. Assume thatelectrons. travel from theelectrodesllL-which may. bea cathode, to theelectrode I I; which may be an anode. ing electron transit an imagecharge, appearson the electrodes equal in magnitude tothe total chargepresent at any moment within the interelectrode space. I he division ofthe image charge. between the two electrodes depends,-in general, uponthe instantaneous distribution of charges moving within theinterelectrode spaceandupon the configurationof the electrodes. Thecurrent induced in an electrode due to motion of a charge is equal totherate of time variation of the induced image charge on the electrodedueto the moving charge. The total instantaneous current induced in theelectrode by the electron stream will be found by summing. theindividual currents induced by all charges moving within theinterelectrode. space. If a voltage exists between electrodesv l0 andthe displacement current due to the interelectrode capacitance must bealso taken into account. i ,1

' Consider now. a three-electrode system formed, for example, by acathode ID, a control grid l2 and the plate I] of a triode. Two spaceshave to be considered. The total current induced in the. intermediateelectrode 12 (Figure 2) is contributed by moving charges in both spaces,Ill-I2 and l2-l Land the total current is equal to; the

vector sum of the two currents. The power generated or absorbed by theelectron stream within the spaces I 0-! 2 and 12-! I depends upon therespective current, voltage and the phase angle between the current andvoltage in each space. Thus the pews: generated or absorbedwitinimthe.spaces lll-i2 audit-41, will be:

' In a more general case, such as a low-u triode,

when there may exist considerable--penetratipn 4 then, under idealconditions, passes through zero and becomes negative. In the case ofcircuit shown in Figure 4 the variation of electron loading with transittime will be as shown in Figure 6. Starting with its maximum value atlow frequencyythe loading decreases-"with:- increasing frequency:

These curves indicate that for certain values of electron transit angle,that is for certain values of the electric fields from space "FF-f Einto space V I0l2, one must also consider direct-interaction intoaccount.

In order to reduce the electron loading .the, total power must bereduced to a minimum;

This can be accomplished bychoosingcurrents,

voltages and their respective phases in-isuch a way that the totalpower;

W='W1,2+War-}:Wa.-1+- V 1 isa'mininmm; I

In -aconventional negative grid tetrodeopen' ated-at lowfrequenciestheinputelectrode load-- ing' wili jbe negligibly small" ifthe. driving voltage is -appIied in a conventional manner-between'thegrid and the cathode so--that* the voltage also voltage presentinthis'regicn 'and" hence no negative power -is*-develope'din the G- Sspacetc' balance the powenabsorbeclin the G-G space; As'the drivingfrequency is increased-the circuit of" 'Ffgm-e'-- 3 will exhibitelectron loading which initially wilI-increase-withfrequency. Thisloading :is 'due -to-- the-fact that i withincreasingefectron-transit-time with-respect to tr period of thefirivingfrequencythe 'amplitudes and phasesoi= currents'in the C-Ga-nd G S spaces' changein such a =manner that the amounts of *power ab sorbedand generatedthe-two spaces no longerbalance eacn other; For the'case ofa high icontrol grid when the spacings and DA): voltages aresuch thatthe=--G'-S" electron transit time isnegligible compared'*' to- 0-6?transit time ananalysis shows that the: electron loading c'enductancelwill vary with= transit time as shown in; 'Figurefis Here theordinatesof the curve represent the ratio 'G/Gmo where G conductanceof the--grid- G' due to: electron motions and G'mptransconductance of the grid*6- at very: low "orzero frequencyy that is :whemsthe transittimeof theelectron is negligilzile in comparison to the time of one cycle oftheifrequency 01 the applied :voltage; The ahscissae represent the-ratio: 'r/T,-" that is =the- 'ratio -;of the; transit time oftheielectron tok the period ofazoscillatiorr of. the applied alternating:voltage. 'Ihei:electrorr loading: innreasesrapidly) Wiflh'; transit:time.

reaches a maximumiat the-value of; atransit-ti-me 1-. equal 1020.85: ofthe .csciilationtzperiod I. and

How

,of theratiopi l transit time the loadingrwiik beismall even forconventional input. circuits. However, the values of frequency andopfimtihg voltages for these optimum conditions frequentlytlieloutsidethe useful operating range of the tube. The tubes could be designedfor-this optimum condition but, in general, this may necessitate acompromise, so that high transconductancesmay be pantiy sacrificed: Thepresentrinvention provides :means' --for vneutralize ing 6136110119loading: for "at wide 2 range --offre quencies-.- and: operatingvoltages-r Without. any: sacrifice of the useful characteristics ofthe-dime,v such as highvtransconductancee I AA general: scheme is:Jbhatt aim addition to. the

driving voltagesappliedzbetweena the cathode and grideawcltage developedbetween the control.

grid and the screen ofn-suolr' a; magnitude and" phases, as:tm-generateepower win the-grid-screen space and :this :p'owereis, fedrbackrinto the. oath-- odeegridtcincuity sothat; ic-.wil1 balance thei power absorbedrin :ithecathodeegridrspace.

- zip-schematic adiagram of-fsuch: aicircuit is. rep-.

resented dug-Figural 7: Anoimpedancezzais in-.-

tnoducenzbetweenithe screen Sr-andrthegrid ;G of. suchomagnitudeeandiphase angle; :that the cur+ rent'z'oes produce a: roltagesvr acrossthis, inreratedsin the G=S space isrthenrfedto the --grid.-; cathodecircuit Z1 by means ofamouplingz-circuit Zae The simpedances Z2. and Z2usually take the iormnofntuned; circuits; and the coupling impede ance:Zlt ;maybe :the. inter-electrode ccapacitance onranauxiliary-couplingelement;i

- A modification Ofcthe circuit shown'im-Fi'gurer'lissrcprtesented:.schematically in; Figure 8, where: the impedancesZzda-showmi-ntroduced .between 0 thescreem-Szand;the-cathode G ratherthan betweenathescreen- Sr. andrthe, control gridrG. The coupling.betweennthe circuitsziiand Z2 is 'pro-: videdr' by tli'etcontrol-l 'gridto'screencapacitance 011% :can ibe'supplemented byanzam-riliary con-.2

- pling ch'icuiti zm ln FigureszsTandl 8 conven tiimalo output :cireuim:with: output impedancea (Z).- :connect.ed; betweenirthe anode and thescreen-.- are shown. H'cwevera; OthEIJtYDGS-"Of output circnits :can':be -usedn sinceethe 'g-input. loading neutralizationschemevhereaproposed-inrno -way -dependssupomithe eextractiontof:"energy from the outputvcircuitl 1 Fiancee-.9 'nhows'sschematically 1the I input loadmementralizationwircuit in combination; with: aninductiveetype-zoutpntucircuitz: Here the outputcircuitnisrjconnectedibetween-:the :two screening electrodes'si S2,; Thesuppressor: and current collectmgrelectrodes, representedrespectively-by S3: and-coll,- a-realsoishow-nu Figure 10. representsschematicaliy; the input; a circuit arrangement of. Figures 8: incombination-1 with the inductive-. output circuit. In theeabove circuitdiagrams oniyxthe essential; 2: circuitsltare-eindicated. Blocking;munding. ;and-o,,by passing condensers which: are used-:foc;providingisolation ,ofelece trodes for D. 0., so that differentD.-C. voltages can be applied to difierent electrodes, are not shown.

One practical embodiment of my invention incorporated in a so-calledinductve output tube" is shown in detail in Figure 11. Inductive outputtubes and their operation are described more fully in my United StatesPatent 2,237,878, issued April 8', 1941, and assigned to the RadioCorporation of America. Briefly this tube comprises a cathode forsupplying a beam of electrons and a collector for receiving theelectrons. A modu lating grid is placed adjacent the cathode formodulating the beam of electrons which passes to the collector.Surrounding the beam path is a resonant cavity circuit comprising ahollow memher having a passageway extendin therethrough through whichthe beam passes. The passageway is provided with a gap lying in a planetransverse to the beam path. As the modulated beam of electrons passesacross this gap, energy is transferred from the beam to the resonantcavity circuit-which provides the output circuit for the tube and whichcan be coupled to a radiator or to an amplifier. 1

Referring to Figure 11, the tube is provided with a concave surfacecathode l5 which can be made of tantalum. This cathode is heated byelectron bombardment from an auxiliary cathode l6 made for example inthe form of a tungsten spiral and surrounded by a focusing shield or cupI! for directing the electrons from the filament to the cathode it. Thecathode spiral I6 is supplied with heating current by means of leads l8and I9 and the main cathode I5 is supported at the end of a tubularmember I5 to which the oathode lead is electrically connected. Theelectron beam is modulated by means of the grid 2| and passes through apair of screen and accelerating tubular electrode members 22 and 23separated by gap 24 and the electrons are collected by means of acollector electrode 25 which is provided with a cooling jacket 26 forcooling the collector. The accelerating and screening electrodes 22 and23 are cylindrical and conically shaped to avoid absorbing electroncurrent from the beam which may tend to spread. The output circuit is ofthe closed resonant cavity type and is formed by two conically shapedmetal surfaces 21 and 2'|"joined at the periphery by a short cylindricalsection 211. The gap in the resonant cavity registers with the gapbetween the accelerating electrode members 22 and 23 to which theconically shaped sides of the resonant cavity are secured andelectrically connected.

In order to practice my invention the cathode I5 is mounted in thesupporting tubular member 29 of cylindrical form, a collar 28 ofinsulating material serving to insulate the tubular cathode extension l5from the tubular'member 29 but permitting capacity couplingtherebetween. Thus the leads for the heater and cathode are shielded bymeans of the tubular member 29 which serves as the inner member of aconcentric line circuit. The control grid 2| is supported at the end ofthe tubular member 30 of cylindrical form surrounding and coaxial withthe inner tubular member 29 to form the outer portion of the concentricline circuit, the ends being closed by disc members 3| and 3|. Thecathode gridcircuit is formed by the tubular members 29 and 30 whichconstitute the inner and outer conductors of a concentric line shortedby the closure disc 3|. This cathode-grid circuit, which may be referredto also as a resonant cavity tank circuit, correspondsto impedance z ofFigure 9. r The large capacitance between the cathode support or ex-'tension l5 and cylindrical member 29 serves to by-pass radio frequencycurrent from the cathode to the tubular member 29. I

The closure member 3| is provided with an aperture throughwhich the leadwires l8, l9 and 2!! extend and a collar or extension 32 to which theinsulating cup-shaped member 33 is sealed and through which theconductors pass and are sealed. The cup-shapedmember 33 hermeticallyseals the interior of the circuits.

A third tubular'member 34 of cylindrical form is co-axial with andsurrounds the other two tubular members- It is provided with closuremembers 34 and 31, a gap 22 being provided between the closure member3'! of tubular member 34 and closure member 3| of tubular member 33. Thespace between the cylinders 30 and 34 forms a resonant space whichprovides an impedance equivalent to Z2 shown in Figure 9 between thecontrol grid and accelerating or screen electrode 22.

To provide an insulating support between the accelerating and screenelectrodes 22 and 23 to which a high positive voltage is applied inoperation and the grid 2! to which a negative bias is applied, thecylinder 34 is supported on the wall of the tank circuit by theinsulating glass cylinder or collar'35 sealed to the cylindrical collarmembers 36 and 31 supported on the cylindrical member 34 and the wall21' of the tank circuit respectively. High capacitance between the endportion 31 of the cylindrical member 34 and the adjacent wall of thetank serves to by-pass high frequency circulating current so as toreduce the radio frequency potentials between the tubular member 34and'the wall of the tank to a negligible value.- The collector 25 issupported in like manner from the other wall of the tank circuit towhich is attached the collar extension 38, the collector cooling jacketbeing provided with collar extension 39, both sealed to the insulatingcylindrical member or collar 40.

Independent tuning of all circuits is provided by means of plunger typecondensers, for example the outer tubular member 30 is provided with acollar or extension 4| surrounding an aperture in the outer surface ofthe tubular member. Sealed-to this extension is a re-entrant insulatingtube 42 extending through this aperture and an aperture in the innertubularmember 29pmvided with an extension 43 surrounding the aperture.This re-entrant glass tube is preferably made of low loss glass or ofquartz. The tuning plunger 44 is inserted within the re-entrantinsulating tube and may be adjusted by means of the insulating rod 45attached to the plunger. Varying the position of the plunger changes thecapacitance between the adjacent circuit elements and thus affords ameans for tuning of, the internal circuits. For tuning the screencircuit the same kind of arrangement is provided at 46, the tubularmember'34 being provided with an aperture around which extends collar4|, the re-entrant glass tubing extending within the cupshaped extension43' in the tubular member 30-. A like arrangement is shown generally at41 in the tank circuit.

The coupling between the cathode-grid and grid-screen circuits, whichcoupling corresponds to impedance Z0 in'Figure 9, is provided by meansof closed loop 50, the position of which is adjustable by means ofadjusting rod 5|. An extension 48 on the outertubular member 34surrounds an,

members I36 and I31 connected at their peripheries by means of thering-shaped member I38. Thus a second resonant cavity is providedsurrounding the resonant cavity of the cathodecontrol grid circuit. Theaccelerating or screen electrode I21 is secured to the wall I31 of thescreen electrode-control grid circuit. The resonant cavity outputcircuit comprises the side wall I31, the side wall I39 and the'outerring member I40- connected at the peripheries. The ring members I40 andI38 could of course be extensions of each other. The acceleratingelectrode I28 is connected to and supported by the end wall I39. I

A coupling and tuning of the circuits is permitted in the same manner asin the other modifications of applicant's invention, that is theenvelope is provided with a number of re-entrant portions extendingthrough'apertures in the various tank circuits and providing passagewaysfor coupling loops or tuning condensers. The driver circuit is coupledto the grid-cathode circuit by loop I4l extending within re-entrantportion MI". The screen electrode-control grid tank circuit and thecontrol grid-cathode tank circuit are inductively coupled to permitfeedback by means of the loop I42 within extension I42. This loop ismounted within the re-entrant portion I42 of the envelope extendingthrough apertures in the two tank circuits. Tuning of thecathode-control grid tank circuit is accomplished by means of the tuningplunger I43 slidably mounted within the re-entrant tube I44 extendingthrough apertures in the tank circuits and the extensions I33 and I34between which is provided a gap. Tuning of the screen electrode-controlgrid circuit is accomplished by means of the tuning plunger I45 mountedwithin the re-entrant glass tube I46. The plunger I45 enters a tubularmember I49, which is attached to member I34, and also projects into atubular well I50 connected to the electrode I21. A similar arrangementis provided for tuning the output circuit, the plunger I41 beingslidably supported within the re-entrant tube I48 and couplingextensions II and I52. The output is delivered by means of the loop I41mounted within the extension I48, which extends through an aperture inthe ring-shaped connecting member I43 of the output tank circuit.Heating current is supplied by means of potential source I52 andpotential difference for causing bombardment of the rear surface of thecathode I20 by voltage source I54. Grid bias is furnished by means ofvoltage source I53. The potentials required for the tank circuit and thecollector are provided respectively by potential sources I55 and I55.

in Figure 13 for example the resonator comprising the slightlydishshaped or cone-shaped walls I31-I39 closed at their peripheries bymeans of the collar-like element I and having the axially tubularextension I28, is that in case these resonators become heated duringoperation and expansion occurs, the walls I31 and I39 will move in thesame direction, that is toward the right, keeping their same relativepositions and the relative position of the tubular member I28 so thatthe gap width varies little if any. Thus, although the resonator may besubjectedto temperature changes, its resonant frequency remainssubstantially constant.

It will be apparent from the above discussion and description that Ihave provided an electron discharge device particularly suitable for useat ultra-high frequencies since both ohmic and radiation resistancelosses due to high radio frequency circulating currents-in electrodesand leads have been substantially eliminated, and because electronloading, which results from-interaction of the electron stream and thecircuit, including regenerative or degenerative effectscaused by leadimpedance, has also been substantially neutralize. This is accomplishedby means of leads and external conductors of highly. conducting materialandlarge diameter. The radiation losses are reduced to a minimum bythoroughly shielded circuits comprising closed type cavity resonators.These resonators are provided with novel and effective means for tunmg.

While I have indicated the preferred .embodi ments of my invention ofwhich I am now aware and have also indicated only one specificapplication for which my invention may be employed, it will be apparentthat my invention is byno means limited to. the exact formsillustratedor the use indicated, but that many variations may be made inthe particular structure used and the purpose for which it is employedwithout departing from the scope of my invention as set forth in theappended claims.

What I claim as new is:

1. A resonator including a hollow conducting member having an aperture,a conducting member supported on the wall of said resonator andsurrounding said aperture, a cup-shaped conducting member supported froma portion of the inner wall of said resonator and registering with saidtubular member and said aperture and a reentrant member of insulatingmaterial sealing said aperture and extending through said tubular memberand into said cup-shaped member, and a plunger-like conducting memberextending within said re-entrant member of insulating material andmovable longitudinally of the tubular member and cup-shaped member.

2. A first resonator including a first hollow conducting member havingan aperture therein, a second resonator including a second hollowconducting member surrounding said first hollow conducting member andhaving an aperture registering with the aperture in said first hollowconducting member, a tubular shield element extending from the wall ofthe first hollow conducting member through the aperture in the secondhollow conducting member and surrounding said aperture, and meansextending through said tubular shield element into the interior of saidfirst resonator for coupling purposes, a first tubular member withinsaid first resonator supported on a wall portion of said first resonatorand extending toward the opposite wall and a 11 second :tubularmember:positioned on the oppo site 'wall -o't' said first resonator andregistering: with said firsti tubular member, and conducting means:movable longitudinally of. said tubular members for tuning said' firstresonator:

A- first resonator including afirst hollow conductingmember l'iavingtanaperture-therein; a seeond resonfior including a-second ho'llowconducting member surroundings-aid' in st hollow oondueting= member andhaving an aperture registering:- with the :aperture in said firsthollowconducting member; a tubular shield element extending. from thewall of the first hollow conducting member through the aperture inthesecond-hollow conducting-member and-surrounding said aperture, and meansextending: through saidtubul'ar shield element into: the interior ofsaid first' resonator for coupling-purposes, arfirst' tubular memberwithin said first resonatorsupportedon a wall 'portionofvsaid firstresonator &

and extending-toward the -opposite wall-and a second tubular memberpositioned on. the oppositewall of said-first resonator andfregisteringwith said first tubular member,- and'" conducting means movablelongitudinally of saidi tubular s members fbrtuningsaid first resonator;and a first tubulabmeans supported withimsaidfsecond' liolloweonduetingmember-and between said first hollowconducting-memberand saidseconcfhollow Conducting member, and-a seeond'tubul'an means supportedwithin said second 'hollow conducting member and registering with: thefirst tubular means within said second hollow conducting member, andconducting means moving longitudinally-of saidtubular means for tuningsaid second resonant cavity tank circuit:

first resonatorincluding a: first hollow conducting-member havingarr-aperture therein, a-seeond=resonator-including a second hollowccondueting= member. surrounding said? first hollow I2 eendli'cting--member, a:firsttubular memhenwithe in said-first hollow conducting"memberand -sup ported on: a wall and extending :t'oward 'thetopnor sitewalrandia second"-tubulanmemberpositioned ing member and registeringnmth: said first-tuba lar member, and conducting means1i'n'ovalcile lonegitudinally: of said'wtubular members: for tuning saidi'first;resonator; andi a first tu'lmlarmeairrs supported-J within: said second?hollow-eoml1mting.- member andebetween;saidafirstr liollow conducting:member'and'said'second hollow eonduntingrmezmber, anda: sec-0ndtuhulanm'eansmupportecb-mithx in said. second hollow conducting; memberregistering; with the first tubular: means within saidrsecondhollowcon-ducting member; .andfeoneducting? means moving;longitudinally;- of: :saitb tubular means forrtuningsaideseoondlresonatnm andsa third aperture-within said 'finstthoilowmoneductingv memberiandoa; coupling: loopy: extending between said? hollow.conducting: members tor coupling: setichrestimators.-v

GIEIZEIL The iollowine .ref rences.-.areaoineoondin the fileof thispatentg V

